LED lamp tubes have the advantages of environmental protection and high efficiency, and have gradually replaced traditional fluorescent tubes. The general LED tube does not have the dimming or lightness adjustable function, which affects the use experience. To solve this problem, for example, CN108633142A discloses a dimming circuit for an LED lamp, including a constant voltage source, and an LED load connected in series to the output of the constant voltage source. The switch tube at the end, the driving circuit electrically connected to the switch tube, and the driving circuit drives the switch tube to be turned on and off under normal conditions to perform PWM lightness adjustment on the LED load.
For example, CN208445794U discloses a dimmable LED lamp driving circuit, which comprises a DC/DC conversion circuit, an LED lamp string and a switch tube driving circuit, and the DC/DC conversion circuit is connected to the LED lamp string through the switch tube Q1, the switch tube Q1 is connected to the switch tube driving circuit; the circuit is combined with a frequency modulation chip and a switch tube driving circuit to adjust the frequency of the switch tube, thereby adjusting the brightness of the LED string.
Another example is CN105554956A, which discloses a PWM lamp illumination system based on dimmable PWM, including a rectifier circuit, an output driving circuit, a PWM dimmable circuit and an LED illumination source. The rectifier circuit converts the alternating current into direct current, and sends it to the output driving circuit, which will be outputted through the output driving circuit. The output voltage obtained by the action is loaded on the dimmable control chip of the PWM dimmable circuit to provide power supply for the chip, and the dimmable control chip determines the on/off of the internal power switch according to the PWM signal provided by the port, and changes output current of the LED light source.
The above LED tubes regulate the current flowing through the LED source by changing the duty cycle of the PWM signal, but most of the LED tube control devices only have a power switch. Thus, it is important to find out how to dim the LED tube through the power switch.